The surgical transplantation of organs has been successfully performed since 1960 owing to the improvement of surgical techniques, the introduction of by-pass circulation and the development of drugs that suppress immune rejection of the donor organ. At the present time, the donor organ is harvested under sterile conditions, cooled to about 4° C. and placed in a plastic bag submerged in a buffered salt solution containing nutrients, and finally transplanted into the recipient. The solution is not oxygenated and is not perfused through the organ blood vessels.
The lack of donor organ availability, particularly hearts, lungs, and livers, is a limiting factor for the number of organ transplants that can be performed. At the present time, less than 25% of patients who require a heart transplant receive a new heart, and less than 10% of patients who require a lung transplant receive one. A major consideration is the length of time that a donor organ will remain viable after it is harvested until the transplant surgery is completed. For hearts, this interval is about four hours. The donor heart must be harvested, transported to the recipient, and the transplant surgery completed within this time limit. Thus, donor hearts can be used only if they are harvested at a site close to the location where the transplant surgery will take place.
It has long been known that organs will survive ex vivo for a longer time if they are cooled to 4° C. and actively perfused through their vascular beds with a buffered salt solution containing nutrients, and that ex vivo survival of an isolated organ can be further extended if the solution is oxygenated. Several factors play a role in the prolonged survival. At 4° C. the metabolism is greatly reduced, lowering the requirements for nutrients and oxygen, and the production of lactic acid and other toxic end products of metabolism are also greatly reduced. Circulation of the perfusion fluid replenishes the oxygen and nutrients available to the tissue, and removes the lactic acid and other toxic metabolites. The buffered solution maintains the pH and tonic strength of the tissue close to physiological.
Perfusion that allows the transport of a harvested organ from a site removed from the location where the transplant surgery will be carried out requires the use of a light weight portable device that operates under sterile conditions for pumping the cold buffered nutrient salt solution through the organ blood vessels, and in which the organ also can be transported from the site of harvesting to the site of transplantation. In order for one person to carry the entire assembly without assistance, and to transport it in an auto or airplane, it should be compact, sturdy and lightweight. The system for loading the perfusion fluid should be simple and allow minimal spillage. There must be a means for oxygenating the perfusion fluid. The device requires a pump with a variably adjustable pumping rate, which pumps at a steady rate once adjusted. Sterility must be maintained. To be completely portable, the device should contain a source of oxygen, an energy source to operate the pump, and should be housed in an insulated watertight container that can be loaded with ice. An entirely satisfactory device is not currently available.
The use of a lightweight, cooled, self-contained perfusion device would have a number of beneficial consequences. (1) The organs would be in better physiological condition at the time of transplantation. (2) Prolonging the survival time of donor organs will enlarge the pool of available organs by allowing organs to be harvested at a distance from the site of the transplant surgery in spite of a longer transport time. (3) It would allow more time for testing to rule out infection of the donor, for example with AIDS, hepatitis-C, herpes, or other viral or bacterial diseases. (4) The pressure on transplant surgeons to complete the transplant procedure within a short time frame would be eased. Transplant surgeons are often faced with unexpected surgical complications that prolong the time of surgery. (5) Better preservation of the integrity of the heart and the endothelium of the coronary arteries at the time of transplantation may also lessen the incidence and severity of post-transplantation coronary artery disease.
On Oct. 12, 1999 the assignee of the present invention was granted U.S. Pat. No. 5,965,433 for a portable organ profusion/oxygenation module that employed mechanically linked dual pumps and mechanically actuated flow control for pulsatile cycling of oxygenated perfusate.
The aforementioned patent contains an excellent description of the state of the art in the mid-nineties and the problems associated with transport systems for human organs. The patent also outlines the many advantages obtained by the ability to extend the transport time from approximately 4 to 24 hours.
Human organ transplantation is plagued by limitations due to insufficient time to transport an organ while maintaining its viability and by an inadequate donor pool. The present invention will significantly diminish the problem of limited transport time by providing an apparatus that will extend the transport time to up to 48 hours. This increased time will inherently increase the size of the donor pool and will allow for extensive disease testing and matching.
The present invention will also greatly reduce damage to the organ being transported and will allow organs from post-mortem donors to be used. Today, organs are only harvested from donors who are brain-dead but whose organs have never ceased to function.
Currently, an organ is transported by putting the organ in a plastic bag of storage fluid, put on ice inside a cooler. In 4 hours, 12% of the transported organs “die” or become unusable, and all the organs are degraded.
A particular advantage of the transport system of the present invention is that it is easily loaded and unloaded by double-gloved surgical personnel and that the fittings require minimal dexterity to assemble and disassemble.
Another advantage of the present invention is that it does not use the flexible permeable membranes of the prior art that, due to their constant flexing, are subject to fatigue stresses and rupture with catastrophic results.